A known and effective technique for determining the microbe or enzyme concentration in a sample involves combining the sample with a substance that undergoes an oxidation-reduction reaction in the presence of the microbe or enzyme, and following the course of the reaction utilizing an electrochemical cell. For example in the presence of glucose, many bacteria metabolize methylene blue as an oxidant to produce the reaction product leuco methylene blue. If the reduction of methylene blue to leuco methylene blue occurs in an electrochemical cell, reoxidation of the leuco methylene blue to methylene blue at the cell anode will give rise to a measurable current that can be related to microbe concentration. This technique is described in greater detail in U.S. Pat. No. 3,506,544.
One of the major advantages of the electrochemical method for determining microbe or enzyme concentration is speed. For example, the traditional plate count method for the detection and enumeration of bacteria typically requires from 24 hours to several days to produce results. The electrochemical method, on the other hand, can typically produce results within an hour or less. Even this great speed increase could be further improved, however, were it not for the need to remove dissolved oxygen from a liquid sample solution prior to the introduction of bacteria and measurement of the resulting current. This need arises because oxidation of leuco methylene blue by dissolved oxygen competes with oxidation at the cell anode, and therefore modifies the measured current. In the past, conventional gas spargers have been used to bubble argon or other inert gases through the sample solution prior to the introduction of the bacteria. Such spargers have typically comprised a Teflon tube having small holes drilled in it, such that gas escaping from the tube forms small bubbles that pass upward through the solution. The time required to decrease the dissolved oxygen to the required level in the electrochemical measurement of leuco methylene blue has been typically 15 minutes to over one hour.